1. Field of the Invention
The present invention relates to a thermosetting silicone resin composition for forming a reflector for an LED, a reflector for an LED using the same and an optical semiconductor apparatus.
2. Description of the Related Art
An optical semiconductor device such as an LED (Light Emitting Diode) has now been utilized as various indicators or light sources for a street display, automobile lamp, and lighting for home. A thermoplastic resin such as a polyphthalamide resin (PPA) has been used as a material for a reflector for an LED with a large amount. In recent years, a thermosetting resin such as an epoxy resin using an acid anhydride as a curing agent has also been used as a material for a reflector.
It has already been disclosed in Patent Documents 1 to 5, and 7 to 9 that a thermosetting resin such as a silicone resin and an epoxy resin can be used as a material for a reflector of an LED. A matrix array type reflector has also been disclosed in Patent Document 6.
However, LED devices progress toward a high luminance is rapidly progressing as a back light of a recent liquid display television or a light source for general illumination, and a demand of reliability and durability for the LED is becoming more severe. In a thermoplastic resin such as a liquid crystalline polymer and PPA (polyphthalamide) or a thermosetting resin such as an epoxy resin which have conventionally been used as a reflector, there causes the problems that deterioration of the resin is remarkable in an environment that heat and light are simultaneously received, so that the resin is color-changed and light reflectance is lowered whereby it cannot be used.
In Patent Documents 1 to 3, there are disclosed an epoxy resin and a silicone resin, but there is no detailed description about the resins themselves. In general, a silicone resin includes various ones from a liquid material to a solid material in an uncured state, and further after curing, in a gel state, a rubbery state and a hard resinous material.
It is difficult to use a resin which becomes a gel state after curing for a reflector, but a resin which becomes a rubbery state can be molded to a reflector. When a surface-mount matrix array type reflector is molded on one surface of a metal frame using a resin which becomes rubbery after curing, modulus of elasticity is low so that warpage of the whole board seldom occurs. However, there are problems of causing malfunctions that the package or leads are easily deformed by an external force since they have low modulus of elasticity at room temperature so that wire bonding is snapped, or the interface between the reflector and an encapsulant for an LED is peeled off or the encapsulant is fractured.
On the other hand, when a reflector is produced by using a silicone resin which gives a resinous hard cured product after curing, there is a problem that the whole board is remarkably warped since its modulus of elasticity is high whereby dicing cannot be performed. Therefore, to prevent from warpage, a prescription that a large amount of inorganic filler is filled in the resin composition has generally been performed to put close the expansion coefficient to that of the metal frame. According to this method, fluidity of the resin composition is lowered, so that if a matrix array type reflector is produced by transfer molding, there is a problem that non-filling occurs.
A refractive index of a cured silicone resin itself is generally close to that of an inorganic filler, so that there causes an inconvenience that a light emitted from the light-emitting device leaks outside when a wall thickness of a reflector obtained by molding a reflector material is thin.